Lincoln Electric SVM 117-A service manual Output Rectification, Feedback Control

E-2 THEORY OF OPERATION E-2

to Section TOC	to Master TOC		OUTPUT RECTIFICATION AND FEEDBACK
Return	Return		WIRE	GAS
			SPEED	SOLENOID
							WIRE
							DRIVE
			ARC				MOTOR
			VOLTAGE
			CONTROL BOARD
				G			TACH
				A
				T		GUN TRIGGER AND THUMB SWITCH
		LINE	MAIN	E
				S
			TRANSFORMER
		SWITCH		I			FEEDBACK
				G
				N
TOC				A
	TOC			L
			RECONNECT				POSITIVE
Section	Master
							TERMINAL
					C		CHOKE
					A	F
					P	E
					A	E
to	to
					C	D
			SCR		I	B
Return	Return		RECTIFIER		T	A
					O	C
			FAN		R	K	NEGATIVE
					S
			MOTORS				TERMINAL
						SHUNT

Figure E.3 - Output Rectification and Feedback.

TOC	TOC	OUTPUT RECTIFICATION AND
Section	Master
		FEEDBACK CONTROL
to	to	The AC output from the main transformer secondary
		weld winding is rectified and controlled through the
Return	Return
		SCR rectifier assembly. Output voltage and current
		are sensed at the shunt and output terminals and are
		fed back to the control board. The control board com-
		pares the commands of the ARC Voltage Control
		potentiometer with the feedback signals. The appro-
		priate gate firing pulses are generated by the control
		board and applied to the SCR rectifier assembly. The
		control board controls the firing of the SCRs, thus con-
		trolling the output of the machine. See SCR
Section TOC	Master TOC	Operation. The control board also powers and com-
		mands the gas solenoid and the wire drive motor.
to	to		NOTE: Unshaded areas of Block Logic
			Diagram are the subject of discussion
Return	Return
			WIRE-MATIC 250